Multiple color printing processes require production of color halftone separations which are used to make printing plates corresponding to each color ink to be printed. In a traditional four color printing process it is necessary to produce cyan, magenta, yellow and black halftone separations which are used to make printing plates for printing cyan, magenta, yellow and black process inks, respectively.
Originally, halftone separations were produced on a camera by exposing original color artwork sheets of film through color separation filters and appropriate halftone screens having the desired screen angles and screen pitch. This method obtained relatively inexpensive production of halftone separations, but was tedious, time consuming and required extensive operator training. With the advent of reliable electronic scanners, color separations are no longer produced using a camera.
An electronic color scanner typically includes a rotating scanning drum for analyzing original artwork and an electronic dot generator for exposing halftones. In operation, the color scanner scans original color artwork to obtain red, green and blue color data, processes and stores the information for the entire workpiece, and thereafter electronically exposes cyan, magenta, yellow and black halftone separations. Available electronic color scanners typically utilize a laser dot generator to expose the halftone separations onto film wrapped around a rotating exposure drum. Unfortunately, electronic color scanners are very complex and require substantial training and experience to operate. Electronic color scanners are also very expensive, which makes them economically unfeasible for most printers interested in producing color halftone separations, resulting in the common practice to contract his service to a color separation house.